Abstract

A framework is developed to simulate the acoustic streaming and the formation of conical bubble structures (CBS) in ultrasonic horn reactors. In these reactors, acoustic pressurewaves propagate from the vibrating solid horn to the liquid. On its movements away from the horn, sound is attenuated producing acoustic streaming, which is exacerbated by the presence of inertial acoustic bubbles that diminish the pressure amplitude many fold very near to the acoustic source. This is a complex Multiphysics phenomena occurring at different time and length scales. Inertial bubbles, which have sizes of the order of few micrometers, oscillate, grow, and collapse as function of time within the period of the acoustic wave while acoustic streaming is a time independent hydrodynamic movement of the liquid occurring through the totality of the reactor. The four main phenomena, solid vibration, acoustic pressure, streaming and bubble generation and distribution, are simulated in COMSOL Multiphysics in a stepwise fashion. The first two phenomena are coupled and solved in frequency domain, and the resultant acoustic pressure forces are applied to solve turbulent streaming and a transport equation in time-independent mode. Steps are repeated sequentially until a good agreement is found with experimental CBS, power, and streaming.